High Performance Electrical Connector

ABSTRACT

A socket connector for connecting a post or ball wherein the female element grips the post with resilient prongs with end tips at low insertion force but positive contact is maintained and wherein attempted withdrawal is normally inhibited by increasing force applied to the post by the female element in response to the withdrawal force. The female element comprises a tube of resilient conductive material that has been sliced or helically partitioned into opposing helical prongs so as to allow the prongs of the connector to spirally open around the post or ball-like bump and mechanically grip the post or bump as the post or bump is inserted along the longitudinal axis of the tube. The tubular element may be made by forming helical prongs in the end of a tube in helical cuts from about a mid section to one end of the tube.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/774,725 filed Feb. 17, 2006, on behalf of Decision Track LLC, aSubchapter S corporation sharing common ownership with the presentassignee. The content of said Provisional Application is incorporatedherein by reference in its entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

Not applicable

BACKGROUND OF THE INVENTION

This invention relates to miniature electrical connectors, as forexample ball grid array (BGA) connectors, including connectors havingpin dimensions of less than 1 millimeter in diameter and pin pitches ofless than two millimeters. One or more embodiments of the presentinvention relate to a high performance electrical connector, that is aconnector for supplying high current (relative to connectors ofcomparable size) and high frequency (RF) signals to high performancemicroelectronic devices, for example, and without limitation, integratedcircuits (“ICs”), including microprocessors, chips for peripheralfunctions and RAM memories.

Connectors are used widely in electronics to interconnectmicroelectronic devices such as semiconductor integrated circuits(“ICs”), printed wiring boards, system boards, backplanes and cable ofvarious sorts. A socket is a type of connector used to connect terminalson an electronic device to corresponding contacts on a printed circuitboard or other electrical interconnection means. It is often an array offemale-type elements intended to engage male-type elements of a plugarray. In addition, sockets are routinely used in systems for: (a)testing electronic device performance (an assortment of socket typeshave been developed to connect to a device under test (“DUT”) having awide variety of terminals and configurations), or (b) bum-in ofelectronic devices at elevated temperatures. A cable connector isanother type of connector that is typically used to connect an array ofterminals on an electrical cable to a group of parallel electrical wiredor other conductors. Backplane connectors and inter-board connectors arefurther types connectors used to connect an array of terminals on oneprinted wiring board to a corresponding array of terminals on anotherprinted wiring board.

Prior art connectors are differentiated typically according to contactortype and intended end use (i.e., application). As such, connectors usedin application in sockets are typically designed to make electricalcontact to microelectronic devices having specific types of deviceterminals—types of device terminals contacted by sockets include pingrid arrays (“PGAs”), J-leads, gull-wing leads, dual in-line (“DIP”)leads, ball grid arrays (“BGAs”), column grid arrays (“CGAs”), flatmetal pads (“LAN” grid arrays or “LGAs”), and many others. In order toprovide sockets for microelectronic devices with this variety ofterminals, many contactor technologies have been developed for sockets.In addition to the foregoing, further differentiation among prior artsockets refers to low insertion force (“LIF”) sockets, zero insertionforce (“ZIF”) sockets, auto-load sockets, bum-in sockets, highperformance test sockets, and production sockets (i.e., sockets for usein products). In further addition to the foregoing, low cost prior artsockets for burn-in and product applications typically incorporatecontactors of stamped and formed springs to contact terminals on a DUT.In still further addition to the foregoing, for high pin-count prior artsockets, a cam is often used to urge device terminals laterally againstcorresponding contactors to make good contact to each spring whileallowing a low or zero insertion force.

For specialized applications, prior art sockets have used a wide varietyof contactors, including anisotropic conductive sheets, flat springs,lithographically formed springs, fuzz buttons (available from Cinch,Inc. of Lombard, Ill.), spring wires, barrel connectors, and springforks, among others. Prior art sockets intended for applications wheremany test mating cycles (also referred to as socket mount-demountcycles) are required typically use spring pin contactors of the typeexemplified by Pogo® spring contacts (available from Everett CharlesTechnologies of Pomona, Calif.). Spring probes for applications in theelectronics test industry are available in many configurations,including simple pins and coaxially grounded pins. Most prior art springprobes consist of a helical wire spring disposed between a top post (forcontacting terminals on the DUT) and a bottom post (for contactingcontacts on a circuit board—a device under test board or “DUT board”).

Prior art sockets typically have a plurality of contactors disposed inan array of apertures formed through a dielectric holder. By way ofexample, a high performance, prior art test socket may incorporate aplurality of Pogo® spring contacts, each of which is held in a pinholder with an array of holes through a thin dielectric plate. Thedielectric material in a high performance, prior art test socket istypically selected from a group of dimensionally stable polymermaterials including: glass reinforced Torlon 5530 available fromQuadrant Engineering Plastic Products, Inc. of Reading, Pa.; Vespel;Ultem 2000 available from GE Company GE Plastics of Pittsfield, Mass.;PEEK; liquid crystal polymer; and others. The individual Pogo® springcontacts are typically selected and designed for signal conduction at animpedance level of approximately fifty (50) ohms. In certain highperformance, prior art configurations, the contactor is a coaxial typehaving a center spring pin with a contactor barrel body enclosed withina cylindrical, coaxial, ground shield spaced to achieve a desired signalimpedance, typically fifty (50) ohms.

Connectors used in applications for connecting one printed wiring boardto another printed wiring board can be classified by type including edgeconnectors, pin-in-barrel connectors, stamped spring connectors, springfork connectors, LAN-grid array connectors, conductive elastomericconnectors, and various types known in the art.

Cable connectors adapted to flat cables are generally similar to printedwiring board to printed wiring board connectors with the added featurethat one side of the connection is made to a flex cable or a flat arrayof wires rather than to a printed wiring board. Cable connectors adaptedto a round bundle of wires are generally of the type employing a pin inbarrel wherein a spring in the barrel retains the pin and applies alateral force on the pin to establish reliable electrical contact. Thespring incorporated into the barrel element may be a spring insert, abundle of spring wires or an integral spring in the barrel. The class ofconnectors used for socketing ICs is specialized and important theelectronics industry. The recent growth in use of BGA terminals for ICpackaging has resulted in use of new and varied sockets adapted to BGAterminals for increasing terminal count and area density. BGA socketshave evolved in several directions. One type involves use of a camdriven spring wire to contact the side of each ball. Spring pins orPogo® pins have been adapted to use in BGA sockets for certainapplications in which the high cost of the socket is acceptable.

Low-cost BGA sockets for mass market applications have evolved the useof stamped and formed springs that cradle each ball of the BGA andprovide some measure of mechanical compliance needed to urge a springconnector into contact with a mating ball. Variations of stamped andformed springs are configured to use two or more formed springs to gripeach ball and thereby make positive electrical contact while retainingthe ball mechanically. Miniaturization and density of the mechanicallystamped and formed springs are limited by present capabilities to acertain size. Although advances continue to be made in the manufacturingart of stamping and forming springs, sockets with contactors so made arelimited in density by the complexity of stamping and forming vary smallminiaturized springs. Further, the mechanical compliance of a stampedand formed spring is typically small in a vertical directionperpendicular to a substrate of a ball. Because of small compliance in avertical direction, a miniature stamped and formed spring may be unableto accommodate motion of a contactor support relative to a ball mated toit, thereby allowing vibration, mechanical shock load and forces,flexure, and the like to cause the connector to slide over the surfaceof the ball. It is known in the industry that repeated microscopicmotion of one contact relative to a mating contact causes fritting or abuild up of small, particle debris that can lead to contact failure.

Stamped and formed spring contacts are typically held in an array ofshaped holes through in a molded plastic housing to form a connectorassembly. As connector assemblies are miniaturized, the molding andassembly process are increasingly difficult and costly, thereby limitingthe extension of connectors based on formed spring contacts to very highdensities.

BGA sockets have also been constructed with contactors that makeelectrical contact to a bottom region of a ball by means of bundles ofhelical wires, wires in elastomer material, cantilever springs,lithographically formed flat springs and other contactors that applyforce vertically to a mating ball. The vertical force is necessary tomake a good connection between a ball of a BGA and such contactor issignificant for BGA packages with a large number of balls or bumps. Forexample, the clamping force for a BGA socket that applies forcevertically to 1200 contact bumps is as high as 30 Kg, as needed toachieve adequate contact to each of the contact bumps. The clampingforce needed by BGA sockets that make contact by applying forcevertically is an increasing problem as the number of contact bumpsincreases into the thousands.

As is well known to those of ordinary skill in the art, a primaryfunction of prior art connectors is to provide reliable and repeatableelectrical contact to electrical terminals without causing damage toeither. Further, a connector must provide a low resistance connectionover a product lifetime that involves repeated temperature cycles,mechanical shock, vibration and flexure. As such, contact resistance isone measure of reliability of a connector as determined as a function ofa number of temperature cycles, a number of drops, a number of flexuresand a G-force level of vibration. As connectors are miniaturized,improvements in reliability are needed to meet the requirements offuture electronic systems.

Advances in the density and speed of electronic devices are placingadditional demands on connectors. In particular, a continuing increasein the wiring density of electronic systems requires a correspondingadvance in the density of connectors as determined by the number ofcontacts per unit area. Further, at higher frequencies and clock speeds,the size and the self inductance of connectors are becoming an importantlimitation to system performance. In addition to a lower inductance,advances in impedance control and shielding are required for futureelectronic systems.

In light of the above, despite the many connector technologies availablein the prior art, there is a need in the art for a connector that cansatisfy one or more of the above-identified demands relating to smallersize, higher density and higher performance.

The following is a listing of patents believed to be relevant to thepresent invention.

U.S. Pat. No. 3,676,838, which is believed to be the most relevantpatent to the present invention, discloses a clamp-type connector havingU-shaped elements in a socket intended to grip ball-like pins of a plug.Despite being of a substantially larger scale than the presentinvention, the structure of the gripping mechanism, particularly asrepresented by FIGS. 5 and 6, rely on a pair of detents in opposingexpandable grips of the receiving socket. Unlike the present invention,the gripping mechanism does not tend to tighten only upon attemptedwithdrawal of the pin but relies on the boundaries of the detent tomaintain position in the socket. If the detents and balls are ofnon-matching or of non-uniform size, looseness, non-uniform grippingforce and loss of gripping ability may result.

U.S. Pat. No. 5,887,344 is another example of a ball pin fitting intodetents of a gripping socket. Folded wings are intended to grip aball-like tip. The invention therein disclosed features many of the samecharacteristics of the '838 patent.

U.S. Pat. No. Re. 36,442 illustrates an adapter for emulating a ballgrid array type package. Pitch dimensions are equal to or greater than 1mm and holes may be on the order of 300 microns. There is no evidentprovision for gripping pins upon attempted withdrawal.

U.S. Pat. No. 5,669,774 illustrates a ball grid array with sockets thathave mounted therein petal-like tines to grip balls of the ball arrayand in that sense is similar to the 838 patent.

U.S. Pat. No. 5,518,410 illustrates a ball to ring contact where thesocket contactor element is rotated by a cam upon socketing.

U.S. Pat. No. 6,264,476 illustrates a wire segment based interposer withcoaxially shielded socket elements, where the wires, if resilient and insome configurations may have a gripping function, around an insulativecore, as for example FIG. 2 and FIG. 3 b, but evidently none isdisclosed or suggested.

U.S. Pat. No. 6,846,184 discloses various types of contacts composed ofsprings that impinge but do not grip confronting contact buttons. Thistype of contact should not be confused with a ball gripping arraysocket.

Various other ball grid array connectors, banana plugs with splitferrules, interposers, pin arrays and the like are known but arebelieved to be no more relevant than the illustrative patents.

SUMMARY OF THE INVENTION

According to the invention, a socket connector is provided for makingelectrical connection in an array to a metal post and more particularlyto a conductive metal ball wherein the female element of the connectorgrips the post with resilient prongs with end tips in such a manner thatlow insertion force is required but positive contact is maintained andwherein attempted withdrawal is normally inhibited by increasing forceapplied to the post by the female element in response to the withdrawalforce. More particularly, the female element comprises a tube ofresilient conductive material that has been sliced or helicallypartitioned into prongs at a pitch within a selected range of pitches soas to allow the prongs of the connector to spirally open around the postor ball-like bump and mechanically grip the post or bump as the post orbump is inserted along the longitudinal axis of the tube. The prongs ofconnector tube makes effective electrical contact at several locationsaround the circumference of the ball. The tubular element according tosome embodiments is made by forming resilient helical prongs in the endof a tube in at least two helical cuts (forming opposing prongs) throughthe tube from about a mid section to one end of the tube.

The female prongs of the connector according to the invention preferablyare able to grip a ball around its maximum circumference so as to retainthe ball within the tube. By fabricating helical prongs on an end of ametal tube by means of laser cutting techniques, a miniature connectormay be made that is able to socket a ball as small a flip chip bump,i.e., on the order of 200 microns diameter. The connector according toembodiments of the invention is able retain a ball held within resilienthelical prongs to make good electrical contact notwithstanding vibrationand mechanical stress.

Numerous benefits are achieved using the present invention overconventional connectors. For example, an embodiment of the presentinvention provides a means for contacting a dense array of bumps, suchas solder balls, with a connector that is only slightly larger than theball and therefore bumps can be more densely spaced than in the priorart. For example, a connector made by laser cutting a thin wallstainless steel tube can be made with an outside diameter only 100microns larger than the diameter of the ball, allowing the spacingbetween connectors to be very small in order to form a high densityarray of connectors.

A further advantage of the present invention is provided by a tubularconnector with helical prongs on a first end that engage a first balland helical prongs on a second and opposing end that engage a secondball, whereby the prongs of the first end resiliently pull the firstball toward the second ball. This advantage enables use of an array ofsuch connectors to attach an electronic device to a substrate withoutneed for a mechanical retaining component to apply force urging thedevice toward the substrate.

Yet another advantage is provided by the present invention embodied in aconnector that has a low self inductance. Thin laser-cut grooves throughthe tube allow less magnetic flux penetration into the interior of thetube than a connector made of a helical wire spring. The self inductanceof the connector of the present invention may be further reduced bymaking the helical prongs short, as they extend a small distance from asolid girth around the tubular connector. These and other aspects of thepresent invention allow a high performance connector.

Depending upon the embodiment, one or more of these benefits may exist.These and other benefits have been described throughout the presentspecification and more particularly below.

Various additional objects, features, and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are perspective views of high performance connectorsaccording to the invention with prongs adapted to gripping a terminalpost with a ball-like bumps of slightly larger maximum outer diameterthan the inner diameter of the connectors.

FIGS. 2A, 2B and 2C are perspective views of double-ended connectorsaccording to the invention with prongs for gripping a terminal post.

FIGS. 3A to 3C are connectors according to the invention for connectionto a corresponding top and bottom post in which FIG. 3A shows theconnector in an unmated configuration, FIG. 3B shows the connector matedwith the bottom post, and FIG. 3C shows the connector mated with the topand the bottom post.

FIGS. 4A to 4F are posts of several designs adapted to mate with aconnector according to the invention.

FIGS. 5A to 5C show a connector assembly and a corresponding ball-typemetal post in several stages of engagement.

FIG. 5D shows a cross-sectional view of an embodiment of a connectoraccording to the invention which is modified so as to grip and morepositively retain a mating ball.

FIGS. 6A and 6B show cross-sectional views of an embodiment of aconnector according to the invention with a coaxial ground shieldconnector and a mating metal terminal post and ground contact, which inFIG. 6A is in an unmated position, and in FIG. 6B is in a mated position

FIGS. 7A to 7C show an array of connectors according to the invention,wherein FIG. 7A is a side cross-section view of the array alone, FIG. 7Bis a side cross-section view with connectors engaged with a mating toparray of posts and a mating bottom array of posts, and FIG. 7C is a topplan view of the array.

FIG. 8A is a cross-section view in perspective showing a connectoraccording to the invention attached at a collar around its mid sectionto a carrier sheet.

FIG. 8B is a cross-section view in perspective showing a connectorattached by solder to a via in a circuit board.

FIG. 9 is a perspective view of an array of connectors according to theinvention mounted in an enclosure to form a terminal block.

FIG. 10 is a perspective view of an assembly of a microelectronic devicemounted and electrically connected to a system substrate by means of aplurality of connectors according to the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

According to the invention, a high performance connector is provided formaking reliable electrical connection to miniature and typically closelyspaced terminals on an electronic device. More particularly, embodimentsof the present invention provide a cylindrical metal tube that is cut ina helical pattern of slots into several prongs that are adapted tocontact a terminal post around its circumference and to provideelectrical contact thereto.

As illustrated in FIG. 1A, connector 18 comprises a hollow cylindricalmetal tube which is cut through by helical slots 10 to form in thisinstance four canted prongs 12 terminated in four tips 14. Prongs 12 areheld in place by cylindrical collar region 16 in the unsliced portion ofthe tube. The prongs are adapted to grip a post inserted along the axisof connector 18. The posts (not shown) preferably have a ball tip.However, a cylindrical or frustoconical tip having an outer diameter inthe mating region that is slightly greater than the inner diameter ofthe tube is also believed to be within the reasonable spirit and scopeof embodiments of the invention. In accordance with one or morepreferred embodiments, connector 18 is made from a tube of Type 304stainless steel having an inner diameter of 440 microns and 550 micronsouter diameter. Such stock material is available from K-Tube Corporationof Poway, Calif. Four helical slots 10 are cut by making 20 micron widecut lines along a 750 mm (as measured along the tube axis) helical patharound the tube using for example a Nd—YAG laser. Slots 10 are typicallycut at an angle of 35° with respect to a plane perpendicular to the axisof tube 16. Alternatively, slots 10 are measured at an angle of 55° withrespect to the axis of tube 16. However, slots 10 cut at between 15° and75° to the plane are within the contemplation of the invention. Anglesless or greater than these do not effectively promote operation of theprongs. After laser cutting, the tube is plated with a 4 micron thicklayer of nickel and a 1.5 micron thick layer of soft gold to form ahighly conductive surface for contacting a mating post. The steel coreprovides sufficient resilience to grip while the tube 18 is expanded toaccommodate prongs inserted along its longitudinal axis. The connectorof FIG. 1A is intended to electrically connect with and physically gripa 500 micron diameter metal ball as a prong or at or near the tip of aninserted prong. The upstream side of the ball, being of a smallerdiameter is subjected to less retaining force than the equatorial ormaximum outer diameter of the ball. Thus, if the ball is attempted to bewithdrawn, the force from the prongs on the ball increases, particularlyas the helical prongs are induced to unravel around the tube axis,thereby offering enhanced resistance to withdrawal. In fact, force ofwithdrawal causes the prongs to stretch and resulting in increasedinwardly directed force as the prongs attempt to decrease the innerdiameter spacing of the tube. In a specific embodiment, as for examplein FIGS. 3A to 3C, the ball 40 is a steel ball plated with a flashcoating of nickel and a coating of 2 micron thick soft gold. A force of10 gf is sufficient to insert the 0.5 mm diameter metal ball into thecontactor tube and to provide a contact resistance of about 0.018 ohms.Once engaged, the ball 40 may be held in place by the contactor withoutneed of a clamp or other mechanical holder.

Although the embodiment of FIG. 1A shows four prongs 12, it will beevident to one of skill in the art that the contactor may incorporateany plurality of prongs of two or greater as necessary to grip a post orball around its circumference with balanced radial forces. This is to bedistinguished from the alternative of a tightly-packed coil spring,where the end would correspond to a single prong and thus not be able tooffer the gripping leverage of opposing prongs at the end of the tubularstructure. For example, contactor 28 in FIG. 1B incorporates two prongs24 with distal ends ending in tips 22 and with proximal ends attached tothe portion of the tube forming a cylindrical collar 26. Prongs 24 areformed by cutting helical grooves through the wall of a cylindricalmetal tube. The insertion force for mating a bump with contactor 28depends upon the angle of the cut line 20, which in this embodiment ispreferably at angle between 15° and 75° and more preferably between 20°and 70° as measured with respect to a plane perpendicular to the axis ofthe tube. Further benefit may be derived from varying the angle of cutline 20 with axial distance along connector 28. For example, the senseof the angle of the helical cut may be alternated from positive tonegative in order to further reduce self inductance of the connector;the sense of the line may be varied over an axial distance to produce aserpentine cut line. In addition, cut line 20 may vary in width alongthe axial length of the cut.

The constituent material of connector 18 is also 304 stainless steel ofwall thickness 0.05 mm. The thickness of the tubing material of theconnector is selected to supply a required insertion force for insertionof a post into the connector, and is preferably between 2% and 20% ofthe inner diameter of the tube. The thickness and material of thecylindrical tube may vary depending upon requirements of theapplication. For example, the material may be selected from a groupwithout limitation including stainless steel of various types, temperedsteels, beryllium copper, phosphor bronze, copper alloys of varioustypes, nickel tungsten alloys, nickel chromium alloys, nickel manganesealloys, nickel binary and ternary alloys, titanium alloys, and evennitinol-type alloys. (Nitinol is an acronym for NIckel TItanium NavalOrdnance Laboratory and refers to a family of intermetallic materialswhich contain a nearly equal mixture of nickel and titanium and otherspring materials and which exhibit temperature sensitive springproperties including shape memory and superelasticity.) The connectormay be plated with copper, nickel, cobalt, palladium, gold, and alloysthereof, as well as other conductive films. A high strength conductivefilm coating on the tube, for example and without limitation includingNi—W alloys, Ni—Co alloys, Ni—Cr alloys, Ni—Mn alloys, Ni—V alloys andcombinations thereof, may be used to further strengthen the material ofthe tube. In further embodiments, a connector lubricant may be appliedto the surface of the prongs of the connector to reduce fritting andimprove lifetime of the connector.

In addition, the high performance connector of the invention may befabricated by means including but not limited to; laser cutting oftubular material, plasma etching of tubular material, pattern etching oftubular material, pattern plating of tubular material, layer plating oftubular material, LIGA plating, and combinations thereof. The tubing ofthe connector is typically a cylinder of circular cross section,although oblong, square, or polygonal cross section tubes are alsowithin contemplation of the invention. For example, the tube may be acylindrical tube of circular cross section that has been flattened onfour sides. In a further variation, the connector may be fabricated aspart of a substrate carrier structure. Laser annealing, flash annealing,ion beam treatment, pickling, quenching, heat treating and othertreatments known in the art may be used to improve properties of thespring material of the connector.

Further advantages accrue in embodiments of the invention in which adouble-ended connector is provided in which each of the two ends areinterchangeable or otherwise equivalent. FIGS. 2A, 2B and 2C areembodiments of the present connector in which a bottom end is equivalentto the top end in that the mechanical force needed to mate the top endof the connector to a specified terminal post is substantially the sameas the mechanical force needed to mate the bottom end to the specifiedterminal post. Equivalence of the two ends may be achieved by cutting apattern through the bottom end of a tube that is a mirror image of thepattern cut through the top end of the tube. The pattern may be mirroredby a plane perpendicular to the axis of the tube as in FIG. 2B. Thepattern may be mirrored around a point on the axis of the tube as inFIG. 2A. Additionally, the bottom pattern may be rotated about the axiswith respect to the top pattern without substantially changingequivalence of the operation of the top and the bottom pattern.

Double-ended connectors of FIGS. 2A, 2B and 2C offer significantmanufacturing advantages in the assembly of such connectors into arrays.Individual connectors may be inserted into an array of holes in acarrier sheet by automated equipment without the need for examining andorienting the connector in either an up or down configuration. In thisembodiment, a variety of double-ended connector shapes provideequivalent mating forces to a bump. FIG. 2A is a double-ended connectorin which four prongs on both the top end and the bottom end form a righthanded helix. FIG. 2B is a double-ended connector in which four prongson the top end form a right handed helix and the four prongs on thebottom end form a left handed helix. FIG. 2C is a double-ended connectorin which four prongs on the top end and the four prongs on the bottomend form an angle with the axis of the connector that varies withdistance along the axis to form a zigzag pattern. Although adouble-ended connector with equivalent ends provides advantages insimplifying manufacturing assembly, one skilled in the art willappreciate that a double-ended connector of this invention need not haveends that are mechanically equivalent. For example, in certainapplications it is desirable that one end of a connector remain firmlyattached to a mating post while the opposite end is easily disengagedfrom its mating bump. High performance connectors for these certainapplications will have a top and a bottom end that are not mechanicallyequivalent.

A double-ended connector of the invention provides a means forelectrically and mechanically connecting a corresponding pair ofterminal posts thereby providing a high performance electricalconnection therebetween. FIG. 3A shows a double-ended connector 34juxtaposed between top terminal post 40 and bottom terminal post 44. Inthis embodiment bottom terminal post 44 is a 0.5 mm diameter Sn—Ag_(3.5)solder ball soldered to copper pad 46 on polyimide printed wiring board33. Correspondingly, top terminal post 40 is a 0.5 mm diameter steelball plated with thin Ni/Au and thermocompression bonded to gold platedcopper pad 38 on a via in a polyimide printed wiring board 30. Connector34 is a 2.0 mm long 304 stainless steel tube with an inner diameter of0.44 mm and an outer diameter of 0.55 mm that is cut through along eachof a top and a bottom end into four resilient helical prongs 36 and 38respectively of axial length 0.75 mm. FIG. 3B shows connector 34 afterbeing urged downwardly to engage and mate with bottom terminal post 44.FIG. 3C shows a subsequent step in which top terminal post 40 is matedwith connector 34 by urging board 30 downwardly thereby causing topterminal post 40 to engage with prongs 36 of connector 34. Connector 34in FIG. 3C holds top terminal post 40 and bottom terminal post togethermechanically while connecting them electrically. The mating force ofapproximately 20 grams is reduced considerably by ancillary vibration ofsubstrate 30 during mating of connector 34 to terminal post 44.

As will be appreciated by one skilled in the art, an array of connectorssuch as 34 may be used to electrically and mechanically connect anelectronic device, such as a circuit board 30, to a system such ascircuit board 32 without use of clamps or mechanical constraints.Connector 34 may be configured with prongs 36 and 38 such that whenmated, post 40 is captured and urged downwards by a clamping action ofprongs 36 around post 40. Likewise, with a similar configuration ofprongs 38, post 44 is captured and urged upwards by a clamping action ofprongs 38 around post 44. By means of specific design of prongs 36 and38, connector 34 can be made to draw circuit board 30 toward circuitboard 32 upon mating of posts 40 and 44 with the connector 34. By way ofexample, prongs 36 are more preferably designed to make contact aroundthe circumference of the post 40 at several points that lie on or abovethe maximum circumference of post 40. By this method, a substrate 30 ofa first electronic device may be mounted to substrate 32 of a secondelectronic device without the need for mechanical clamps or constraints.When mated, the connectors 34 draw the first and second electronicdevices together and hold them in place both laterally and vertically.The first electronic device may be demounted by urging substrate 30upward with sufficient force to overcome the retaining force holdingterminal post 40 within connector 34.

In certain applications requiring that connector 34 be permanentlyattached to board 32, connector 34 may be permanently affixed to post 44on substrate 32 by reflowing solder bump of post 44 thereby wetting andattaching connector 34 to post 44 on printed wiring substrate 32. Incertain other applications, the board 30 may be temporarily connected tothe board 32 in order to test the assembled system before permanentlyconnecting board 30 to board 32 by heating the assembly. In thisapplication, bumps 40 and 44 are both formed of solder or solder-coatedmetal balls such that heating causes the solder bumps to flow, therebysoldering pad 46 to prongs 38 of connector 34 and soldering pad 38 toprongs 36 of connector 34. Solder may be prevented from flowing up theprongs 36 and 38 by solder stops, such as oxidized nickel or othersolder stops known in the art.

Terminal posts including but not limited to those shown in FIGS. 4A to4F may be adapted for use with an electrical connector of the invention.Terminal post 50 of FIG. 4A is a solder ball that is soldered to copperpad 54 on printed wiring board 56. Solder bumps are typically sphericalsections shaped by surface tension during melting and reflow of thebump. Solder balls may have a core of solid metal such as a nicke-platedcopper sphere. Solder bumps may also be shaped mechanically into solderposts and columns, as in a column grid array available from IBMMicroelectronics of Burlington, Vt. Solder bumps 50 are typicallyaxially symmetrical.

Terminal post 60 of FIG. 4B is a solid metal ball 62 attached to annularmetal ring 64 on printed wiring board 66 by means of thermosonic orthermocompression bonding. Preferably thermosonic bonding is used toattach nickel/gold plated copper ball 62 to gold plated annular copperring 64. Terminal post 60 is suited for mating with a high performanceelectrical connector of the invention for high temperature applicationsfor which a solder bump is not well suited. Ball 62 is a spherical ballof metal such as without limitation brass, bronze, stainless steel,carbon steel, copper, silver, nickel and alloys thereof. Metallic ball62 may have thin metal coatings of nickel, Monel, gold, palladium,silver, rhodium, osmium, and alloys thereof to protect the ball againstcorrosion. Alternatively, ball 62 may be made of a polymer, glass,hollow polymer, or other dielectric material that is coated with a thinmetal film. Ball 62 of terminal bump 60 may be supplied in varying sizesin order to regulate and control the engage/disengage force for matingto an electrical connector of the invention. For example, a ball with alarger diameter is be mated with a bottom end of connector 34, while aball with a smaller diameter is mated with a top end in order to allowfor relatively easy engagement and disengagement of the top ball fromconnector 34.

Terminal post 70 of FIG. 4C is a metal post 74 with an axiallysymmetrical head 72 and an elongated end that is held in a platedthrough hole 78 in printed wiring board 76. Post 74 is commonlyavailable in the industry as a Swiss machined brass pin. Post head 72has a chamfered or rounded top edge that facilitates mating with a highperformance electrical connector of the invention.

Terminal post 80 is a metal boss 82 made by plating metals such as Ni,Cu, Ni—Ag, Sn—Ag, or other materials known in the electrochemical artonto pad 84 on substrate 86. Tip 70 of terminal post 80 may be made of adifferent metal to facilitate mating with the connector. Thecircumference of post 82 may be made a function of height to furtherfacilitate mating with connector 34. Alternatively, post 70 may be madeby etching a layer of metal such as Cu, Ni, and various alloys to leavea cylindrical boss 82.

Terminal post 90 is a metal ball 92 held above the surface of substrate96 by collar 94. Such an elevated post 90 may provide augmentedmechanical retention properties when mated with connector 34 or otherembodiments of this invention. By way of example, terminal 90 may befabricated by first plating an annular ring 94 on substrate 96. Ball 92may be selected to be a copper ball with thin surface coatings of nickeland gold. Ball 92 is joined to collar 94 by means of thermosonic bondingor thermocompression bonding as is well known in the art of electronicpackaging.

Terminal post 100 provides an advantage of low profile not provided byother terminal posts that project above the surface of a substrate. Post100 is made by cutting an annular ring 104 in a top surface of circuitboard 106. Top 102 of post 100 and side walls 108 and 110 are coatedwith a thin layer of metal such as copper, typically by electrolessseeding and then electroplating copper to a desired thickness. Terminalpost 100 provides a recessed surface 110 that mates with connector 34.

FIG. 5B shows mated connector assembly 130 according to one or moreembodiments of the invention, while FIG. 5A shows components of assembly130 before mating. A ball 122 is attached to substrate 126 by collar124, thereby providing a terminal post for mating with connector 132.Connector 132 comprises a metal tube in which a top end is cut by one ormore spiral slots from a mid section of the tube to the end, therebyforming resilient helical prongs 134. Prongs 134 remain attached to amid section of the tube at a proximal end and are free to flex at adistal end. Connector 132 is attached to substrate 120 at a bottom endheld in plated hole 140 by solder 146. A wire 148 is connected throughvia 142 to connector 132 by solder mass 148. Ball 122 is mated toconnector 132 by urging substrate 126 downward, thereby displacingresilient prongs 134 outwardly away from the axis of connector 132.Prongs 134 contact ball 122 around its circumferential girth at a heightwhere the circumference of ball 122 is near a maximum. The prongs 134urge inwardly upon ball 122 to make positive electrical contact with theball and to grip the ball and retain it within connector 132. Two ormore resilient prongs contact the ball at two or more points around itscircumference.

Connector assembly 130 provides electrical contact that is resistant toshock and vibration. Resilient prongs 134 grip ball 122 and flex toallow the ball to move in a lateral and in a vertical direction withoutloosening its grip on ball 122. Mechanical stress, vibration, mechanicalshock, warpage, and thermal cycling cause prongs 134 to flex while theyretain a grip on ball 122. By way of example FIG. 5C shows substrate 126after being moved vertically, thereby exerting stress on connector 132and causing resilient prongs 134 to flex and extend in a verticaldirection. Whilst prongs 134 distend and flex vertically, they retain agrip on ball 122 that allows continuous electrical contact. Further,flexure of prongs 134 significantly reduces rubbing of the ball againstconnector 132 due to vibration or other mechanical stress on assembly130. A reduction of rubbing or “fretting” of ball 122 against surfacesof connector 134 improves the reliability and extends the life ofconnected assembly 130. Fretting as caused by rubbing of one metalsurface against another metal surface is well known in the art toproduce fine particulate debris at the site of contact, such debrisdegrading the electrical reliability of an electrical connection betweenthe two metals. Preferably, to reduce fretting, the resilient prongs 134are formed by two or more slots cut at equal intervals around thecircumference of connector 132, where each slot is cut at an angle ofbetween 15° and 75° and more preferably between 20° and 70° with respectto the axis of the connector. Additionally, and more preferably,resilient prongs 134 are formed by slots cut to a length measured alongthe an imaginary line on the midpoint of the slot that is at least aslong as half of the outer circumference of the tube of connector 132.

A further improvement 152 of connector 132 acts to draw ball 122 intothe connector in a direction along its axis. FIG. 5D shows connector 152as improved by modifying the slots 158 between each prong 154 so as towiden the slot 158 with distance away from the top end of connector 152as measured along the its axis. An increase in the width of each slot158 with distance from the top end of connector 152, at a region whereball 122 contacts prongs 154, causes prongs 154 to pull ball 122 furtherinto connector 152. The inwardly directed force on ball 122 is due to aflexure of prongs 152 with movement of the ball along the axis ofconnector 152. The inwardly directed force on ball 122 is due to flexureof prongs 154 caused by a widening of slot 158 with distance away fromtop end of connector 152. In order to cause an inwardly directed forceon ball 122, it is not necessary to emboss prongs of connector 152, toslope the walls of the tube of connector 152, to curl the prongs 154toward the axis of the tube, or other distortions of the tube. The innerand outer walls of tube of unmated connector 152 are straight andparallel to the axis of the tube. Unmated connector 152 comprisesportions of a right regular cylinder, the walls of which are aprojection of a loop along the axis of the cylinder. Preferably the loopis a circle and the cylinder is a right circular cylinder. Becauseconnector 152 exerts an inward or compressing force on a mating ball 122without the need for dimpling, embossing, twisting or otherwisedeforming the tubular body of the connector, the connector 152 is easilyfabricated by laser cutting a tube with a specific pattern consistentwith one or more embodiments of the invention.

According to one or more embodiments of the invention, tubular connectorelements may be configured in a coaxial connector assembly 200 as forexample shown in FIG. 6B. Coaxial connector assembly 200 includesterminal post 186 on top substrate 180, terminal annulus 182 on topsubstrate, an inner connector 190 attached to conductive receptacle 212on bottom substrate, and an outer connector 198 attached to conductiveannular receptacle 206 on bottom substrate 208. In one or moreembodiments of the invention, inner connector 190 is electricallyconnected to a signal wire 204 by solder 202 linking wire 204 toconductive receptacle 212. Wire 204 may be the center conductor of acoaxial cable—not shown in order to facilitate illustration ofprinciples of the invention—for which a coaxial shield is electricallyconnected to conductive receptacle 206. The coaxial connector assembly200 provides a high performance signal connection for which a signalcarried by inner connector 190 is shielded from ambient electricalinterference. Assembly 200 also provides a connection of controlledimpedance approximately Z_(o)=60 ln(D/d), where D is the inner diameterof outer connector 198 and d is the outer diameter of inner connector190.

FIG. 6A shows coaxial connector assembly 200 before mating. AlthoughFIG. 6A shows both outer connector 198 and inner connector 190 affixedto bottom substrate 208, the inner conductor may be affixed to a bottomsubstrate and outer connector 198 may be affixed to a top substrate.Alternatively, both inner connector 190 and outer connector 198 may beaffixed through an interposer sheet such that the top ends of the innerand outer connectors extend above the interposer sheet to mate withcontact terminals on a top substrate, and bottom ends of the inner andouter connectors extend below the interposer sheet to mate with contactterminals on a bottom substrate. Mechanical vibration, such asultrasonic vibration, acoustic vibration, impulse shock, and the likemay be used to facilitate mating or de-mating of the connector.

Coaxial connector assembly 200 offers advantages in provides a simplemechanical coaxial connector that may easily be miniaturized. One ormore embodiments of the coaxial connector are self locking and do notrequire clamps, clips, bayonet bases, clamshell holders or other meansof holding the mating contacts together. It will be understood that incertain applications an added mechanical restraint or clamp may bedesirable for assuring that the mating connectors remain mated underconditions of high mechanical stress. Further advantages accrue due tothe mechanical compliance of connectors 190 and 198 that enablemaintenance of reliable coaxial electrical contact during shock,vibration, thermal transients, and mechanical stress. It will beunderstood by one of ordinary skill in the art that connectors 190 and198 may be double-ended, where a top end and a bottom end aremechanically equivalent, in order to simplify volume production assemblyof coaxial connectors, because the tubular connectors may be orientedeither up or down before being attached to substrate 208. With these andother advantages, one or more embodiments of the coaxial connector maybe used for high performance connections between circuit board, formounting high frequency microelectronic devices, for making temporaryconnection to an electrical system for purposes of testing, forconnecting one coaxial cable to another, and other applications thatwill be obvious to one in the industry.

FIG. 7A is a cross sectional view on section line A-A′ of an embodimentin which a connector array 320 of double-ended connectors 300 isdisposed in holes through a carrier sheet 316. In this embodiment,double-ended connectors 300 have a top end and a bottom end which areequivalent in that the force required to insert a given post into theprongs 328 the top end of connector 300 is substantially equal to theforce required to insert the same given post into prongs 338 on thebottom end of connector 300. Four resilient helical prongs 326 areformed by four spiral slots 304 extending from a mid-section 342 ofconnector 300 to the top end of the connector. Proximal ends of prongs338 are attached around collar region 342 at the mid-section ofconnector 300, while distal ends are free to flex. When a post isinserted downward along a longitudinal axis of connector 300, resilientprongs 326 flex outwardly, away from the axis, in order to accommodatethe post and to contact the post around its circumference.

Each of connectors 300 is held within a hole in carrier sheet 316,whereby a top end of connector 300 extends upward perpendicularly fromthe carrier sheet and a bottom end extends downward perpendicularly fromthe carrier sheet. Each of connectors 300 is a stainless steel 304 tubewith four spiral slots 302 and 304 extending from a collar 342 around amid-section to each end of the tube. Slots 302 and 304 are 0.05 mm wideslices made by a Nd—YAG laser through a 0.05 mm thick wall of the tube.In a typical embodiment, slots 302 and 304 are slanted at an angle of30° with respect to a plane perpendicular to the longitudinal axis ofthe tube. The tube of connector 300 is 2.0 mm long, with an innerdiameter of 0.44 mm and an outer diameter of 0.55 mm. Each connector 300is attached to a carrier sheet 316 by adhesive 318 joining the carriersheet 316 to a collar 342 around the midsection of each connector.Carrier sheet 316 comprises a top metal layer 308 of 0.05 mm thick Be—Cualloy 172, and a bottom metal layer 306 also of 0.05 mm thick Be—Cualloy 172, the pair of which sandwich a bondply dielectric film 310laminated therebetween. Adhesive 318 is a B-staged epoxy that has flowedoutward from the bond-ply dielectric material 310 comprising layers of a0.05 mm thick B-staged epoxy, a 0.05 thick film of polyimide, and a 0.05mm thick B-staged epoxy. A first group selected from connectors 300 ofconnector array 320 is connected electrically to top carrier metal layer308 by metal tabs 312. Details of the attachment of a connector of afirst group to carrier sheet 316 are more clearly illustrated in a crosssectional perspective view of FIG. 8A, showing metal tabs 312 held byelastic deformation of the tabs against collar 342 around the midsection of the tube. Metal layer 308 may connect the first group ofselected ones of connector 300 to a power distribution circuit or aground distribution circuit. Additionally, a second group selected fromconnectors 300 of connector array 320 is electrically connected tobottom metal layer 306 by metal tabs 314. Metal layer 306 may connectthe second group of selected connectors 300 in common to a grounddistribution circuit, a power distribution circuit, a shielding circuitor other common circuit. The top view of connector array in FIG. 7Cillustrates the common connections of a first group of selectedconnectors to a top metal layer by tabs 312, and other commonconnections of a second group of selected connectors to a bottom metallayer by tabs 314 (shown dashed).

Carrier sheet 316 holds an array of connectors 300 in predeterminedpositions. In addition to the construction of an embodiment describedabove, it will be understood by one of ordinary skill in the art thatother configurations of a carrier sheet may be used to hold connectorsof the invention. By way of example, carrier sheet 316 may comprise; oneor more layers of dielectric material such as polyimide, G-10, Ultem®(available from GE Polymers), glass reinforced epoxy, metal reinforcedepoxy, liquid crystal polymer materials, and other polymers; and one ormore adhesive materials including but not limited to B-staged epoxy,FEP, PFA, Ultem®, acrylics, PTFE, polyethylene, polyamide, and polyamideblends. The adhesive material may be used in sheet form; in layered formsuch as bondply laminates; in stencil printable paste such as B-stagedepoxy available from CTI, Inc. of Baltimore, Md. in dispensable adhesivematerials; and other adhesive materials known in the art. The carriersheet may be further be formed by embossing, punching, drilling,stretching, and mechanical shaping to fit specific applications.

In further variants, carrier sheet 316 may include one or more metallayers that may provide thermal conductivity, ground plane connections,power plane connections, electromagnetic shielding, control of thermalexpansion, mechanical rigidity, intra-connector shielding, impedancecontrol of connectors, pressure seals, integral capacitors between metallayers, radiation shielding, means for mounting for discrete components,substrates for additional wiring layers, over-voltage protectiongrounding, stress relief springs, and other applications known in theart. Although FIGS. 7A-7C show thin metal layers 306 and 308, the metallayers may be of any thickness, including a first metal layer thatextends from a mid-section to the top end of connector 300 and a secondmetal layer that extends from the mid-section to the bottom end ofconnector 300. Such thick metal layers are used to provide shielding ofone connector from other connectors. By way of example, the diameter ofthrough holes may vary, with a first hole diameter for power and groundconnectors and a second hole diameter for signal connectors. A metallayer may be connected to selected ones of the connectors 300 by meansknown in the art including without limitation, spring actuated contact,soldering, thermo-sonic bonding, laser welding, conductive adhesivejoining, press fit mounting, and diffusion bonding. A metal layer may beinsulated from other ones of connector 300 by means of an insulatingsleeve on the mid-section of the connector, a dielectric coating on themetal layer, an electrodeposited dielectric coating on the metal layer,dielectric adhesive material, an air gap, and other insulative meansknown in the art. Selected ones of the metal layers may be connected tocircuits that provide power, ground, signals, clock timing, chassisground and other electrical means.

Connectors 300 shown in FIG. 7A-C are double-ended wherein the top endand the bottom end of connector 300 are mechanically equivalent. Incertain applications, it is desirable that the top end of the connectorrequires a low force to engage and disengage a ball post while thebottom end of the connector requires a high force to engage anddisengage a similar ball post. For example, it may be desired that aconnector remain engaged to a bottom ball post when a top ball post isdisengaged from the connector. In this example, the prongs on the bottomof the connector are designed to be stiff and the prongs of the top ofthe connector are designed to be less stiff. Stiffness of a prong may belessened by making the slots wider, making the tube wall thinner,changing the number of prongs around the connector, making the pronglonger, and making changes in the prong shape as guided by mechanicalmodeling.

Connector array 320 is used to connect mechanically and electrically afirst array of posts 326 on top substrate 322 to a corresponding secondarray of posts 336 on a bottom substrate 332. The connection is made byjuxtaposition of the first array of posts on top substrate 322 overconnectors 300 in connector array 320, juxtaposition of the second arrayof posts 336 on bottom substrate under connectors 300 in connector array320, and urging top substrate 322 downward toward bottom substrate 332.Thereby posts 326 on top substrate 322 are mated with prongs 328 on topends of connectors 300 wherein each of prongs 328 contacts a post 326around its circumference, and posts 336 are mated with prongs 338 onbottom ends of connectors 300. After the connection is made, connectorarray 320 holds top substrate 322 and bottom substrate 332 togethermechanically without the need for a clamp or other restraining means,although such means may be added as an additional protection againstdamage by mechanical shock.

Connectors 300 hold mating post 326 on top substrate 322 and mating post332 on bottom substrate 332 together resiliently whereby post 326 maymove a small amount in a horizontal direction and a small amount in avertical direction with respect to post 336 without losing electrical ormechanical connection therebetween. In one or more embodiments, topsubstrate 322 may be moved with respect to bottom substrate 332 by 0.5mm in a horizontal direction or by 0.5 mm in a vertical directionwithout losing contact between posts 326 on top substrate 322 and posts336 on bottom substrate 332. The relative motion of top substrate 322with respect to bottom substrate 332 is accommodated by flexure ofresilient prongs 328 extending from collar 324 to the top end ofconnectors 300, and by flexure of resilient prongs 338 extending fromcollar 324 to the bottom of connectors 300.

After mating, an upward force applied to top substrate 322 acts tostretch prongs 328 of connectors 300 upward without losing connectionwith posts 326, and to stretch prongs 338 of connectors 300 downwardwithout losing connections to posts 336. Resilience of prongs 328 and338 enables connectors 300 to maintain electrical and mechanical contactbetween posts 326 and posts 328 notwithstanding vibration, mechanicalshock, thermal mismatch, acceleration forces, gravity, and other stressbelow a certain threshold. Connectors of one or more embodiments of theinvention are able to withstand a force on post mated to a connector of20 grams before breaking contact therebetween. In order that prongs aresufficiently resilient, the angle of slot 304 between prongs 328 isbetween 15° and 75° or more preferably between 20° and 70° as measuredwith respect to a plane perpendicular to the axis of the connector. Morepreferably, each slot 304 between prongs 328 has a length as measuredalong its midpoint that is at least one half of the circumference of thetube of connector 300, each as measured on the outer diameter of thetube. In addition, the mechanical properties of retention of a postengaged with connector 300 are enhanced by making the width of slot 304increase with axial distance from top end 366, and likewise making thewidth of slot 302 increase with axial distance from bottom end 368. Theincrease of the width of slot 304 with distance from the end ofconnector 300 acts to produce an inwardly directed force on a matingball that is exerted by prongs 328 contacting the circumference of theball as the ball moves along a region of the axis of connector 300.Preferably the ball is mounted to a substrate in a way such that themaximum circumference lies above the surface of the substrate to whichthe ball is mounted. Although posts including but not limited to posts50, 60, 70, and 90 of FIG. 4 are preferred, the connector will operatesatisfactorily for a wider range of post geometries.

Practical use may be made of the invention in mechanically attaching andelectrically connecting one electrical device to another. FIG. 10 showsassembly 420 comprising electronic device 428 mounted to a printedwiring substrate 426 by means of an array of connectors 422. Each ofconnectors 422 has two or more upwardly oriented prongs that grip a ball(not visible) of the BGA on the bottom surface of device 428. The arrayof connectors 422 retains device 428 in position without the need formechanical clamping means to maintain contact during periods of normalmechanical stress. Optionally, a clamp may be added to protect theconnections to device 422 against incidents of high mechanical stress.Resilient prongs on connectors 422 flex to protect device 428 againstvibration and mechanical shock applied to substrate 426. A furtheradvantage of the invention accrues due to the mating properties ofconnector 422, wherein the force needed to disengage an array of matedconnectors 422 from a BGA is greater than the force need to engage thearray of connectors to the BGA. Thereby connectors 422 made according toone or more embodiments of the invention are able to retain electronicdevice 428 against disengagement forces that are greater than the forceinitially used to engage the device. This further advantage enables easymounting of devices on a substrate with a small force, whilst retainingthe device against the effects of larger forces of shock and vibration.Disengagement of device 428 is facilitated by use of vibration,ultrasonic energy, or the like to reduce the force needed fordisengagement of device 428 from substrate 426.

Connectors 422 according to one or more embodiments of the invention aresuited for use in connector arrays for attaching a BGA device to asubstrate. By way of example, without limitation, connector 422 may beconnector 300 of FIG. 8A, connector 370 of FIG. 8B, and connector 152 ofFIG. 5D. Connector 300 is a double-ended connector attached to a carriersheet, as described above. Connector 370 is a double-ended connectorattached at a bottom end by solder connection 372 to via 382 insubstrate 386. Connector 370 of FIG. 8B provides advantages in assemblyin that either end of connector 370 may be soldered to via 382 withoutthe need to orient the connector up or down because each end ofconnector 370 is equivalent to the opposite end. FIG. 5D shows connector152 with slots 158 that increase in width with axial distance away fromthe top end of the connector. This increase in width acts to produce adownward force on a mating ball such that the ball is pulled downwardlyover a range of vertical position for which the width of slot 158increased with distance from the top end of connector 152.

By way of example, FIG. 9 illustrates another application of one or moreembodiments of the invention in which connectors 402 are arrayed interminal block 400. A pair of connectors 402 is held in a cavity 406 inhousing 410. Housing 410 may have a metallic surface so as to shieldelectrically connectors 402 against electrical noise in the environment.Connectors 402 are adapted to mate with a corresponding set of posts ina mating terminal block (not shown). Although each connector 402 retainsa posts mated thereto without need of a clamping force, terminal block400 is provided with mounting lug 412 and mounting screw hole 408 toprovide additional mechanical stability when screws from a matingterminal block are attached through holes 408. It will be understood byone of ordinary skill in the art that any number of contactors may bedisposed in each cavity. The connectors 402 may be single ended ordouble-ended in accordance with one or more embodiments of theinvention. Other connector configurations, shielding methods, mountingmethods, clamps, and brackets will be obvious to the practitioner in thefield.

The invention has been explained with reference to specific embodiments.Other embodiments will be apparent to those of ordinary skill in theart. One of ordinary skill in the art would recognize many variations,modifications, and alternatives. It is therefore not intended that thisinvention be limited, except as indicated by the appended claims.

1. A multiple-contact electrical connector for making electrical contactwith a micro-scale electrically conductive male mating element forelectronic device connections, said connector comprising: a tubularelement having an inner diameter less than a maximum outer diameter of amating post; and at least two slots helically cut in said tubularelement, said slots forming at least two electrically conductive helicalprongs terminating at a first end of said tubular element, said helicalprongs being operative to impose mechanical resistance on said post uponattempted removal of said mating element from said tubular element. 2.The connector according to claim 1 wherein the mating element comprisesa ball and wherein the tubular element has an inner diameter less thanthe maximum outer diameter of said ball.
 3. The connector according toclaim 2 wherein the prongs have a longitudinal thickness on the order ofless than the radius of said ball.
 4. The connector according to claim 1wherein the mating element comprises a metallic post, and the innerdiameter of said tubular element with said prongs is less than the outerdiameter of said post in regions where the prongs abut the matingelement when inserted between said prongs of said tubular element. 5.The connector according to claim 1 wherein the tubular element is slicedat an angle between 15° and 75° to a plane normal to the longitudinalaxis of the tubular element.
 6. The connector according to claim 1wherein the tubular element has been sliced by a laser to form saidplurality of prongs.
 7. The connector according to claim 1 wherein theplurality of prongs in said tubular element has been formed by at leastone of the following processes: laser cutting of tubular material,plasma etching of tubular material, pattern etching of tubular material,pattern plating of tubular material, layer plating of tubular material,LIGA plating of the tubular material.
 8. The connector according toclaim 1 wherein said tubular element is a hollow cylinder having acircular cross section and wherein angle of said slices varies withposition along said cylinder.
 9. The connector according to claim 1having a second end opposing said first end and wherein said second endand said first end are interchangeable.
 10. An electrical connectordevice including elements: a. a cylindrical tube with a wall ofelectrically conductive material; b. said tube having a top end and abottom end; c. a bump of electrically conductive material proximal tosaid top end; d. said top end of said cylindrical tube being dividedinto two or more prongs by helical cuts through said wall; e. saidhelical cuts arrayed at an angle with respect to a plane perpendicularto the axis of said cylinder; f. whereby said prongs engage said bumpthereby making electrical contact at several points on said bump.
 11. Aconnector device as in claim 10 wherein said bump is a solder ball. 12.A connector device as in claim 10 wherein said bump is a plated metalpost.
 13. A connector device as in claim 10 wherein said bump is a metalball attached to a metal contact.
 14. A connector device as in claim 10wherein said bump is a solder ball placed on a metal post.
 15. Aconnector device as in claim 10 wherein said bump is a solder ballplaced on a metal post.
 16. A connector device as in claim 10 whereinsaid bump includes a cone of insulating material with a thin metalcoating.
 17. A connector device as in claim 10 wherein said bump is athin metal sheet that is stamped and formed into a post.
 18. A connectordevice as in claim 10 wherein said bump comprises a cylindrical pin. 19.A connector device as in claim 10 wherein said cylindrical tube has acircular cross section.
 20. A connector device as in claim 19 whereinsaid angle of said helical cuts is between 15° and 75° with respect to aplane normal to a longitudinal axis of said connector device.
 21. Aconnector device as in claim 20 wherein said angle of said helical cutsvaries with position along the cylinder.
 22. A connector device as inclaim 10 wherein said cylindrical tube has a square cross section.
 23. Aconnector device as in claim 10 wherein said cylindrical tube has anelliptical cross section.
 24. A connector device as in claim 10 whereinsaid bottom end is divided into two or more prongs by helical cutsthrough said wall.
 25. A connector device as in claim 24 wherein saidtop end and said bottom end are interchangeable.
 26. A socket formicroelectronic devices with ball grid array terminals, said socketincluding; a. a dielectric substrate with a top and a bottom surface; b.one or more contact cylinders with a top and a bottom end; c. each ofsaid contact cylinders having a thin metal wall; d. said top end of eachof said contact cylinders having two or more helical cuts through saidwall; e. one or more metallic contact pads on said top surface, each padshaped so as to mate with said bottom end of each said contact cylinder;f. said bottom end of each of said contact cylinders permanently affixedto said contact pad; g. whereby each of said contact cylinders is inelectrical contact with a mating said contact pad.
 27. A socket as inclaim 26 wherein said contact pad is formed on a cylindrical depressionin said top surface of said substrate.
 28. A socket as in claim 26wherein said contact pad is formed on an annular depression into saidtop surface of said substrate.
 29. A socket as in claim 26 wherein saidcontact pad is a circular electrode on said top surface of saidsubstrate.
 30. A socket as in claim 26 wherein a ground shield isdisposed above said top surface in space between said contact cylinders.31. A coaxial connector device for making shielded electricalconnections, including; a. a first dielectric substrate with a topsurface and a bottom surface; b. a conductive signal contact cylinderwith a top and a bottom end wherein said top end is cut into two or morehelical prongs and said bottom end is affixed to said top surface ofsaid first substrate; c. a conductive shield cylinder with a top end anda bottom end wherein said bottom end is affixed to said top surface ofsaid first dielectric substrate; d. said shield cylinder positioned soas to surround said signal contact cylinder; e. a second dielectricsubstrate with a top surface and a bottom surface; f. a conductivecontact post on said bottom surface of said second dielectric substrate;g. whereby electrical contact is made between said top end of saidsignal contact cylinder on said first substrate and said post on saidsecond dielectric substrate when said second substrate is urgeddownwardly onto said first substrate.
 32. A connector assembly adaptedto making connections to an array of conductive bumps, said connectorassembly comprising; a. a thin sheet comprising one or more layers; b.an array of two or more holes through said thin sheet; c. a plurality oftubular contact elements each with two or more prong tabs disposed at atop end of said tubular contact element; d. wherein each of said tubularcontact elements is held in one of said holes by an attachment aroundits circumference; and e. whereby said top end of said tubular contactelement faces upward away from said thin sheet.
 33. A connector assemblyas in claim 32 wherein said thin sheet includes a conductive groundlayer.
 34. A connector assembly as in claim 32 wherein selected ones ofsaid tubular contact elements are connected electrically to saidconductive ground layer.
 35. A connector assembly as in claim 32 whereinsaid one or more layers includes a conductive ground plane and aconductive power plane with an insulating layer therebetween.
 36. Aconnector assembly as in claim 35 wherein first selected ones of saidtubular contact elements are connected electrically to said conductiveground layer and second selected ones of said tubular contact elementsare connected electrically to said conductive power layer.